A Note on Causes of Effects

: Interest in applying counterfactual logic to legal settings has resulted in disagreements regarding the proper interpretation of the legal term but for, as in It is more probable than not that the injury would not have occurred but for the defendant action (Robertson, 1997). Let A = 1 stands for the defendant's action, R = 1 for the observed response (e.g., injury or damage), and R0 (respectively R1) for the value that R would have had the action not taken (A = 0). The standard interpretation of the but for criterion is captured by the inequality PN greater or equal to 1/2 where PN stands for counterfactual probably PN = P(R0 = 0/A = 1,R = 1) (1) termed probability of necessity in Pearl (2000a).